The present invention pertains to the art of friction element assemblies, such as clutches and brakes, for automatic transmissions of motor vehicles and, more particularly, to reducing stress in parts of a friction element assembly by providing stress-relief grooves in a pressure plate located in the friction element assembly.
An automatic transmission of a vehicle generally includes an input shaft and an output shaft. The input shaft receives an input torque from a power source, such as an internal combustion engine or an electric motor. The transmission then converts the input torque to an output torque. The output shaft transmits the output torque to the wheels of the vehicle in order to propel the vehicle. The transmission converts the input torque to the output torque by adjusting a gear ratio (for example, during an upshift or a downshift) between the input shaft and the output shaft. This adjustment is accomplished by applying or releasing friction element assemblies, such as clutches or brakes, in order to change torque relationships by altering planetary gear configurations of the transmission.
In a typical transmission for a motor vehicle, the friction element assemblies include multiple interleaved plates and friction members. During operation of the vehicle, in order to apply a friction element assembly, a piston assembly contacts and then applies a force to compress the plates and friction members together to transmit torque through the friction element assembly. For this compression to occur, movement of the plates and friction members must be restricted in some way to provide a force opposing the force applied by the piston assembly. Generally, a pressure plate retained by a snap ring is provided for this purpose, although other portions of the transmission are sometimes used when allowed by the structure of the transmission.
During assembly of the transmission, the friction element assembly is installed followed by the snap ring. The snap ring is usually retained in a mounting groove located in a housing of the friction element assembly and keeps the pressure plate from moving. When the friction element assembly is actuated, the piston assembly compresses the interleaved plates and friction members against the pressure plate. The pressure plate also applies a force to the snap ring, which in turn applies a force to the housing at the mounting groove. As a result, a significant level of stress is applied to the housing, potentially causing the housing to be damaged. Based on the above, there exists a need in the art for a way to ensure the stress level in the housing is kept low so as not to damage the housing.